The Radiation Therapy Oncology Group is a cooperative clinical group of Radiation Therapy Research Centers formed to conduct clinical investigative studies and trials in oncology. Membership is composed of founding member institutions, full members and provisional members, working together on cooperative protocol projects. Actual treatment is carried out at the member institutes with the support of a central administrative and statistical center. The central office also provides internal review of protocols and quality control. Purpose of the organization is the establishment and maintenance of a coalition of clinical radiation therapy centers to develop efficient and economic means for conducting clinical trials in oncology with particular emphasis on radiation therapy. A coalition of centers allows the accumulation of a sufficient number of cases in a reasonable length of time. A critical group is provided to integrate new biologic concepts into clinical investigative programs in radiation therapy. Controversial problems in radiation therapy as well as combinations of radiation therapy with other therapies are brought into clinical trials in an attempt to improve treatment to integrate new biologic concepts into clinical care. The group also provides a means whereby the results of raised clinical trials can be promptly and accurately accessed and advances in radiation therapy quickly recognized and disseminated to other institutions.